Photographic emulsions



Patented June 3, 1952 PHOTOGRAPHIC EMULSIONS Clifford K. Sloan,Thornton, Pa., assignor to E. I.

---1lu"Pont de Nemours & Company, Wilmington, w Del., a corporation ofDelaware No Drawing. Application August 9, 1947, Serial No. 767,862

9 Claims. 1

This invention is concerned with photography "and, more particularly,with the preparation of photographic emulsions. Still more particularlyit is concerned with a process of washing light sensitive hydroxylpolymer emulsions.

Gelatin has been used as the binding agent for silver halide particlesin most of the photographic films and printing papers manufacturedduring the last decade. Since gelatin is an excellent protective colloidwhich forms strong, hard, thin films and the particle size of the silverhalide grains in the gelatin binder can be controlled, it has manyadvantages. Gelatin also serves as a source of certain sensitizingmaterials that are used in obtaining beneficial efiects of speed andcontrast. However, gelatin has a number of disadvantages which placerestrictions upon its use. These disadvantages include (1) a softeningaction that occurs during processing in warm water and (2) a bacterialdecomposition that occurs when stored under hot, humid conditions.Because of these undesirable properties of gelatin, several types ofsubstitutes have been suggested.

Among the proposed gelatin substitutes for this purpose are included theseveral types of synthetic hydrophilic hydroxyl polymers which contain aplurality of recurring intralinear groups, including polyvinyl alcohol,partially'hydrolyzed polyvinyl acetate and their ethers and acetals, andcopolymers with low molecular weightunsaturated compounds, e. g.,ethylene. The manufacture of light-sensitive silver halide emulsionscontaining these hydrophilic synthetic hydroxyl polymers on a commercialscale has presented difiiculties in uniformly removing'the-"watef-solublesalts formed during precipitation of the silverhalide particles. This is because the above-mentioned water-permeable orhydrophilic colloids do'not readily form thermally reversible. gels.Such salts can be easily removed from gelatin emulsions by gelling theemulsions',""shred'ding the*'gelled emulsion, and

for washing. Agglutination of such emulsions by means of sodium sulfatesolutions, acetone, etc., have been proposed but some difiiculty isencountered during the washing and re-solution of the washed emulsion.The coagulated hydrophilic colloid may tend to peptize in the wash wateror tough, rubbery masses may be formed that give slow and unevenwashing. Moreover, when using such agglutination procedures, it isdifficult to secure proper adjustmentof photographic speed and contrastand the final emulsion is likely to contain agglutinates that give agrainy fihn. In addition, the presence of portions of unwashed emulsiontends to give insoluble clumps that show up in emulsion coatings, beingespecially objectionable in thin emulsion layers.

An object of this invention is to provide lightsensitive silver halideemulsions that are substantially free from water-soluble salts andcontain synthetic hydroxyl polymer colloid binding agents. A furtherobject is to provide a practical method of washing silver halideemulsions having such binding agents.

The present invention comprises precipitating light-sensitive silverhalidesin a hydrophilic hydroxyl polymer containing a plurality ofrecurring groups, coagulating the resulting emulsion in the form ofcontinuous filaments by spinning the silver halide-containingemulsionvinto a coagulating bath containing an agglutinating agent,collecting the resulting filaments, and washing the filaments.

In the preferred mode of operation, the lightsensitive silver halideparticles are precipitated in a fluid mixture of the synthetic,hydrophilic hydroxyl polymer by mixing a solution of a water-solublehalide, such as ammonium bromide, with a solution of a water-solublesilver salt, such as silver nitrate, in the presence of the hydrophilichydroxyl polymer. The resulting emulsion may be ripened in this form bythe procedures used for gelatin emulsion and those described in UnitedStates Patent 2,397,866. The emulsion is then coagulated by spinningthrough a small orifice, such as is used in the formation of filamentsfor textile use, e. g., rayon, nylon, etc., into a coagulating bathcontaining agglutinating agents, e. g., acetone, sodium sulfate, andmixtures of such compounds. I'he continuous filaments containing thelight-sensitive silver halide particles are then collected and washedwith water to lower the concentration of soluble salts and thereby topromote the desired photographic characteristics. The washed filamentsare then redissolved by warming in water preferably containing a smallamount of ethyl alcohol. The washed emulsion is then digested either inthis form or after the addition of extra hydroxyl polymer binder andsensitizing dyes, and the emulsion coated on a support after thecustomary treatment with color sensitizers and adjustment of viscosity.The above operations are, of course, carried out in the absence ofactinic light. The film is dried, exposed to an object, and the latentimage developed and fixed in the customary manner.

The invention will be further illustrated by the following examples. Theparts are by weight unless otherwise indicated. Wherever required,operations are carried out in the absence of actinic radiations.

EXAMPLE I The following solutions were prepared at room temperature:

Solution A 70 cc. 3 N AgNOs 42 cc. 20% aqueous NH4OH Solution B 74 cc. 3NNH4Br 12 cc. 0.5 N KI 2.6 cc. water Solution 14 grams completelyhydrolyzed ethylene/vinyl acetate copolymer having a mol ratio ofethylene to vinyl acetate of 1:28

112 grams water 14 grams ethanol The ethylene/vinyl acetate copolymerwas prepared as described in Example V of Hanford and Roland, SerialNumber 466,116 filed June 6, 1942, now abandoned, and the copolymer washydrolyzed according to the method described in Example XI of UnitedStates Patent 2,386,347.

An emulsion containing precipitated silver halide particles was preparedby simultaneous addition at room temperature of SolutionsA and B toSolution C at a uniform rate over a period of ten minutes withcontinuous stirring. The emulsion was then spun into a 20% aqueoussodium sulfate solution using a five hole 3.5 mil spinneret, the silverhalide-containing emulsion beingforced through the spinneret by an eightfoot hydrostatic head. The material coming through the spinneretcoalesced to unite the material from the five holes as a single filamentwhich-was then drawn slowly through the bath until suificient mechanicalstrength was developed to permit stretching the filament approximately.300% in the bath. The stretched filament was wound on a bobbin to athickness of one-fourth inch and washed in running water. The silverhalide-containing filaments on the bobbin were then removed andredissolved in alcohol. One hundred and forty grams (140) of additionalcopolymer solution (C) was added. The emulsion was digested and coatedon a paper support. A sensitometric test. showed that the sensitiveemulsion had satisfactory photographic properties including fog, speed,contrast, and top density.

The following solutions were prepared:

Solution A 500,c,c..3,N AgNOs 3.0.0. cc. 20% aqueous NHiOH 600 cc. water4 Solution B 600 grams completely hydrolyzed ethylene/ vinyl acetatecopolymer solution of the same composition as Solution C of Example I510 cc. 3 N NH4Br 420 cc. water Solution A was brought to F. andSolution B to 112 F. and precipitation of the emulsion was made undernon-actinic conditions by adding Solution A to Solution B, withstirring, over a period of three minutes. The precipitated emulsioncontaining light-sensitive silver halide was placed in a pressure vesseland forced under 15 lbs. pressure through a spinneret of the type usedin Example I into acetone. The agglutinated filaments emerging fromthe'spinneret face were allowed to collect in an open-mesh basketimmersed in the acetone coagulation bath and were then washed by dippinginto water. The light-sensitive filaments were given eight successivewashings in fresh water, allowing ten minutes contact with each washwater before draining. The washed filaments were redissolved by additionof 1130 grams of completely hydrolyzed ethylene/vinyl acetate copolymersolution of the same composition as Solution C of Example I, theemulsion being heated 15 minutes at 65- C. to effect solution. Theconductivity of the emulsion at this point was 500 micromhos. Theemulsion was then digested and finished in the same manner as theemulsion of Example I.

EXAMPLE III A magenta color-forming emulsion was prepared using as theprotective colloid the polyvinyl acetal of m-[p-(5-ethylcarbonato-3-methyl-S-pyrazolyl)benzamido] benzaldehyde described in Example III ofMartin, Serial Number 682,137 filed July 8, 1946, now Patent No.2,476,988 of July 26, 1949. The polymer was dissolved by adding 150 cc.absolute alcohol and six drops of I 10% aqueous potassium hydroxide in400 cc. of water to 30 grams of the polymer. To prepare -the emulsion,grams of this polymer solution was mixed with 20 cc. absolute alcoholand the following two solutions added separately and simultaneously overa period of 15v minutes with constant stirring.

Solution A 29 cc. 3. N AgNOs 20 cc. 20% aqueous NHiOI-I 7 cc. waterSolution B 3100. 3 N NI-I4Br 2 cc. 0.5 N KI 32 00. water Afterprecipitation of the silver halide particles, the emulsion was. added asa thin stream to. a. 1060. (:0. volume. of acetone being stirred with aconstant swirling action, The emulsion was added. at the outer edge ofthe acetone agglutinating. mixture and the coagulated filaments. oflight-sensitive emulsion were collected in the center of the coagulationbath. The coagulated. filaments were removedand washed in the samemanner as. that described in Example I. The emulsion was finished byaddition of 100 grams of the polymer solution previously described inthis example, and digested. It was coated Qn film. base and exposed .tolight through a. step wedge. Development ior ten minutes at 20 C. in ap-aminodiethylaniline developer the bottom of a tank at a six foot depthof 20% aqueous sodium sulfate solution. The pressure -at*whi'ch.theemulsion was spun was adjusted so that. buoyant force caused thecoagulated emulsion to reach the surface of :the salt bath in the formof a continuous filament. The filament was then conducted into a secondbath containing 20% aqueoussodium sulfate solution where it a wasstretched 200% and delivered to a third bath where it was washed withwater continuously. The filament was then delivered to a vesselcontaining aqueous ethanol. When the concentration of'silver halide inthe 10% aqueous ethanol solution reached the point corresponding to theconcentration used in finishing the emulsion in Example I, the resultingmixture was warmed to effect solution and the mixture was finished andcoated as in Example I.

In place of the specific hydrophilic hydroxyl polymers described in theforegoing examples, there may be substituted a large number of othersimilar hydroxyl polymers. Among such polymers there may be usedpartially hydrolyzed polyvinyl esters which are usually prepared byincomplete hydrolysis of esters, such as polyvinyl acetate, polyvinylchloracetate, polyvinyl isobutyrate, etc. Ethers of such hydrolyzedesters can be made by incompletely etherifying the partially hydrolyzedpolyvinyl esters. Among such useful ethers are the methyl, ethyl, andbenzyl ethers.

Polyvinyl acetals of such partially hydrolyzed polyvinyl esters can bemade incomplete acetalization of the partially hydrolyzed polyvinylesters in the presence of an acetalization catalyst. Suitable polyvinylacetals include those made from formaldehyde, acetaldehyde,isobutyraldehyde, and benzaldehyde.

Still other useful hydroxyl polymers include polyvinyl alcohols of low,middle, and high yrscosity, as well as their ethers' and acetalscorresponding to those described in the preceding paragraph.

Syntheticlrydroxyl polymers having an average molecularweight (numberaverage) of 10,000 to 100,000 are useful but those having an averagemolecular weight of 25,000 to 50,000 are preferred.

-In addition to the hydroxyl polymer color formers described in ExampleIII, there may be substituted various other polymers which containrecurring color former nuclei in addition to the recurring -CH(EHOHunits. Typical polymers of this type are described in United StatesPatent 2,310,943,

2,320,422, 2,397,865, 2,415,381 and 2,415,382.

The selection of the agglutinating agent is normally made on the basisof economy and efiiciency of precipitation of the emulsion in a suitableform for washing. There are a large number of suitable agglutinatingagents but their efficiency. varies. Apartial list of agents which areuseful includes water-soluble electrolytes, g

- manner.

such as sodium sulfate, aluminum sulfate, sodium chloride,' ammoniumsulfate, ammonium chloride barium chloride, sodium bicarbonate, sodiumdihydrogen phosphate, disodium hydrogen phosphate, magnesium chloride,calcium chloride, aluminum acetate, zinc chloride, zinc sulfate, andcalcium acetate. Theseagents are also useful as coagulating orflocculating agents. Colored materials and materials which cause fog,such as the chromium, iron, copper, cadmium, and cobalt salts and thelike, are normally avoided although they can function as agglutinatingagents. The preferred agents of this type are colorless, inorganic,soluble salts which have no pronounced oxidizing or reducing action andsimilar salts oforganic acids containing less than eight carbon atoms.Another class of agglutinating agents suitable for use in this processis the water-soluble organic solvents which are at the same timenon-solventsfor polyvinyl alcohol. Such materials include acetone,alcohol, methyl acetate, isopropanol, methanol, methyl ethyl ketone. Ofthese, the lower aliphatic alcohols and ketones are preferred.Agents'which combine chemically-with the polyvinyl alcohol and causegelling or cross-linking .are not compr'ehended by the term.fagglutinatingf agent."

The invention, moreover, is notlimited to the specific light-sensitivematerial described'in..the above-detailed examples. On'the contrary,various other simple and mixed silver halides. may be used as thelight-sensitive materials in like Mixtures of silver bromides,chlorides, and/or iodides can be made by adding mixtures of solublesalts of these halides in like manner,

salts of sufiicient solubility include silver sulfamate, silver sulfate,silver citrate, and silver ace- .tate. u

The invention is applied to the emulsion after precipitation of thesilver halide particles by double decomposition of the silver salt. Itis usually advantageous to have a high fraction'of the total binderpresent at this point in order to provide sufiicient material forfilament formation.

It is desirable that the viscosity of the emulsion at this pointbe ashigh as possible to facilitate filament formation although the inventionhas been practiced at ordinary viscosities used "in precipitation of thelight-sensitive silver halide particles. For many purposes it isdesirable to have all of the polymeric binder'present beforecoagulation. I

It is important in the practice of this invention that the orifice ofthe spinneret be sufliciently small so that'rapid contact between theagglutinating agent and the entire body of'the emerging emulsion streamis quickly attained. For this purpose spinneret holes of the size usedin textile'spimiing', i. e., of the order of '2 to 5 mils may beemployed. The mechanical strength of the fiber is attainedby use ofsmall spinneret holes followed by coalescence of individual fibers togive a filament that is self-supporting and which can be drawn out inthe coagulation bath from to 300% to increase strength. A wide set ofconditions is available for conducting the spinning operation. Theproperties of the emerging filaments of emulsion are considerablydifferent from those formed for textile purposes in that they contain arelatively large amount of light-sensitive silver halide par- SMAQiticles; .EIEhe weight ra "o of imbedded silver halide to they-binder inwhich it is imbedded rangesiromlzl to 10:1,; whereas in textilespinrninz :relatively small .amounts of finely divided particles havebeen incorporated in the system for the purpose of ,delustering. The.,vis- -:cosity .of the spinning solutions of this casernay vary .fromi5to .30 and preferably from 10 110 25 centipoises at 25-C.

Furthermore, the viscosity of the light-sensitive emulsions afterprecipitation of silver halide is FIDWBT than that of polymericsolutions .used in textile spinning. The light-sensitive emulsionIlla-merits,v therefore, :set .up initially to a relatively weakfilament and it is :necessary to iv :special care :to their treatmentduring the early stage after spinning while the .large :amountcf waterassociated with thesilver :halide/hydroxyl polymer .mixture is beingidiSSiIlBitGd and mechanical strength developed to permit handlingthercfilaments. The presence of the relatively large amount .of .silverhalide also tends -:to weakenithe filament. It .is, therefore, desirableto provide .special guides :for handling the coagulating :filaments asthey emerge from :the spinner-ct :face. :Such .guides :may take severalforms. including moving rollers and screens that .supportithe :filamentand move .it forward. This motion .can also .be :attained by motion :of:the water-in .the coagulation bath by pumping past 'the spinneret'face. Unlike textile spinning .art, it is desirable that severalfilaments stick together to *form a single, more uniformly :coagulated,and stronger filament than would result irom extrusion of a largerfilament with care -"originahwater to the coagulation bath gives a fiber.for the washing step which is smaller than that of the ordinary gelatinshreds and which contains considerablyless'water than the latter.

The spinnin-g process is ;a continuous oneand lenlis'itselfto acompletely continuousmethod of making fluid emulsions. The :strong=filaments may be continuously washed as in the last example ormayjbebucket washed" as :is ordinarily'practiced with the higherwater-containing ,gelatin shreds. All coagulation,.spim1ing, and

washing operations are conducted "in the ab- E .sence .of light orchemicals that woilkLpromote log in The final emulsions have vall .theadvantages f uniform was'hingincludingihi'gh. speed, high-con- .trast,high top density, with low ,fog.

.As .many widely different embodiments ofjthis .invention can .be .madewithout departing .from I the spirit .and scope thereof, it is to Theunder- .stood that the invention is not .tolbe ,limited,.ex-

.cept as definedlbyltheclaims.

What is claimed is:

.1. .The process which comprises precipitating light-sensitive silverhalides in a fluid mixture of polymeric materials -asynthetichydrophilic .hyidroxyl polymer which contains a plurality of recurringintralinear groups, extruding the resulting emulsion timough a pluralityof orifices having a diameter from 2 to 5 mils into a coagulating 'bath,coalescing the filaments into a fiber, stretching the fiber 100 to 300%of its original length in said both, removing the stretched fiber andwashing :the latter with water to remove the water-soluble crystalloidalcompounds.

12. The process which comprises precipitating light-sensitive silverhalides in an aqueous solution "having a viscosity of 5 to 30centipoises at 25 C. of a synthetic hydrophil ic 'hydroxyl. polymerwhich contains a plurality of recurring intralinear groups in suchamount that the weight ratio .of silver halide to hydroxyl polymer isfrom 1:1 to, 10:1, extruding the resulting emulsion through a pluralityof orifices having a diameter from 2 to 5 ,mils directly into acoagulating bath, coalescing the filaments into a fiber, stretching thefiber 100 to 300% of its original length insaid bath, removing thestretched fiber and washing the latter with water to remove thewater-soluble crystalloidalcompounds.

,3. A process as set forth in claim 2 wherein said hydroxyl polymerpolyvinyl alcoholiiaving an average molecular weight of "10,000 to 100000.

. 4. A .process as set forth in claim 2 wherein said hydroxyl polymer isa hydrolyzed ethylene/vinyl acetate .copolymer.

.5. A process as set iorth in claim 2 wherein said .hydroxyl polymercontains recurring color for-mer nuclei.

6. The process which comprises precipitating light-sensitive silverhalides in an vaqueous solution having a viscosity of 5 to '30centipoises at 25 .C. of .a synthetic hydrophilic hydroxyl polymer whichcontains a plurality of recurring intralinear groups having a .molecularweight off 10,000 to 100,000, in .such amount that the weight ratiocfsilver fhalide to .hydrcxyl polymer qfrom 1:1

' to 10:1, extruding the resulting emulsion throu h a plurality oforifices having a diameter 2 .to 15 mils directly into a coagulatingbath,

coalescing the filaments into .a fiber. :Stretching ithe fiber 1'00 to300% .of its original :length in said bath, removin the shtetchedfiberand groups in such .amount that the weight atio of silver halide tohydroxylzpolymer is :from ,-1:;1 to l'Ozl, extruding the resultingemulsion through a plurality of orifices having -a diameter .from

2 to 5 mils directly into .aecoagulating ibflth. coal- -ese ing-thefilaments into .a fiber, stretching the 9 bath, removing the stretchedfiber and washing the latter with water to remove the water-solublecrystalloidal compounds and redissolving the washed fiber in watercontaining a small amount of ethyl alcohol.

8. The process which comprises precipitating light-sensitive silverhalides in an aqueous solution having a viscosity of to 30 centipoisesat 25 C. of a synthetic hydrophilic hydroxyl polymer which contains aplurality of recurring intralinear stretched fiber and washing thelatter with water to remove the water-soluble crystalloidal compounds.

9. The prcoess which comprises precipitating light-sensitive silverhalides in an aqueous solution having a viscosity of 5 to 30 centipoisesat 25 C. of a synthetic hydrophilic hydroxyl polymer which contains aplurality of reccurring intralinear 10' groups in such amount that theweight ratio of silver halide to hydroxyl polymer is from 1:1 to 10:1,extruding the resulting emulsion through a plurality of orifices havinga diameter from 2 to 5 mils directly into a coagulating bath containingacetone, coalescing the filaments into a fiber, stretching, the fiber to300% of its original length in said bath, removing the stretched fiberand washing the latter with water to remove the water-solublecrystalloidal compounds.

CLIFFORD K. SLOAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,127,573 Sheppard et al. Aug.23, 1938 2,158,825 Lierg May 16, 1939 2,397,866 McQueen Apr. 2, 19462,415,382 Woodward Feb. 4, 1947 2,422,680 Jennings June 24, 19472,474,617 Cline June 28, 1949 FOREIGN PATENTS Number Country Date448,863 Great Britain June 10, 1936

1. THE PROCESS WHICH COMPRISES PRECIPITATING LIGHT-SENSITIVE SILVERHALIDES IN A FLUID MIXTURE OF A SYNTHETIC HYDROPHILIC HYDROXYL POLYMERWHICH CONTAINS A PLURALITY OF RECURRING INTRALINEAR